One protester held a sign of US president Barack Obama's famous 'Hope' poster, edited to show the leader as a spy wearing large headphones. Another sign read: "Betray Snowden, Betray freedom."

The protesters handed a letter over to the US consulate addressed to Consul General Steve Young.

"For many years, the US State Department has publicly supported the cause of internet freedom and criticised other governments for conducting cyber attacks, surveillance and censorship," the letter said.

"We now understand, through recent revelations, that the US government has been operating their own blanket surveillance systems and allegedly conducting cyber warfare against Hong Kong.

"This is a violation of Human Rights of people of Hong Kong and around the world."

Earlier this week, Mr Snowden told the South China Morning Post newspaper that there have been more than 61,000 NSA hacking operations globally, targeting powerful "network backbones" that can yield access to hundreds of thousands of individual computers.

He was quoted as saying there were hundreds of targets in mainland China and Hong Kong.

Hong Kong has a long-standing extradition treaty with the US, but Beijing has the potential to veto any ruling.

Who is Edward Snowden?

Former CIA contractor who leaked information about US spy agencies

He worked for the National Security Agency (NSA) for the last four years

Was employed by various outside contractors, including tech consultancy Booz Allen and computer company Dell

He copied secret documents at the NSA office in Hawaii

He leaked the documents, which expose how the NSA gains information using a secret program called PRISM

Says he leaked the data because he was worried about privacy and internet freedom

"We are going to see a lot of political juggling between two of the biggest powers in the world in order to possibly extradite Mr Snowden," politician and Hong Kong entrepreneur Charles Mok told protesters.

"Who is losing? You and I, all the internet users in the world. Why? Because we in Hong Kong know the best, we live outside of the Great Firewall of China."

The rally comes amid increasing concern in the city over perceived mainland interference.

"It's quite ironic that Snowden thought that Hong Kong has impeccable rule of law. Long time residents here would know that our freedoms are being stifled on a daily basis on every front," pro-democracy politician Claudia Mo said.

"Our rule of law is facing all kinds of political challenges, so good luck to Mr Snowden."

"The most important thing is in defending Mr Snowden. If he can be extradited and be punished, who will be the second whistleblower?" he told protesters.

"There are a lot of Mr Snowdens all over the world. It's like an execution if they grab Mr Snowden and extradite him.

"They will condemn him to hell in a small cell for tens of years."

Following the rally, the city's chief executive Leung Chun-ying said in a statement: "The Hong Kong... government will handle the case of Mr Snowden in accordance with the laws and established procedures."

"Meanwhile, the government will follow up on any incidents related to the privacy or other rights of the institutions or people in Hong Kong being violated," the statement added.

So far the US has not filed a formal extradition request to Hong Kong, a former British colony that retained its separate legal system when it returned to Chinese rule in 1997.

Beijing ultimately retains control over defence and foreign affairs but it and Hong Kong's governments have yet to make any comment about Mr Snowden's case.